This invention relates to apparatus producing machine-direction heat seals for sealing one or more hems in a moving web of thermoplastic film and more particularly to an oven-heated hot wheel sealer for use in the manufacture of draw tape plastic bags.
Bags made of thin polyethylene materials have been used in various sizes. Small bags are used in the packaging of samples and the like. Larger bags are used as shopping bags; and even larger bags are used for containing trash.
A particularly advantageous closure for such a bag includes a draw tape constructed of the same polyethylene material. U.S. Pat. No. 3,029,853--Piazzi and British Pat. No. 1,125,363--Jortikka are examples of draw tape bags. Such closures have been successfully employed in the bags.
Draw tape closures for large trash bags, and the manufacture of these draw tape bags are described in U.S. Pat. No. 4,624,654--Boyd et al and in the related applications identified below.
Forming the hem, into which the tape is inserted, is shown for example in U.S. Pat. Nos. 2,897,729--Ashton et al, 3,058,402--Kugler 3,058,403--Kugler, and 4,617,008--Boyd et al, and in the copending patent application of applicant's assignee "Hem Folder with Integral Tape Inserter for Making Draw Tape Bags,", Herrington, Ser. No. 871,238 filed June 6, 1986.
Draw tape hems have been previously made by various methods. One method is to use a Teflon-coated hot bar which opens and closes against the film in the area of the bag machine where the film starts and stops. The bar closes once during each cycle while the film is stopped. A second method is to blow a series of hot jets against the film as it travels by. Bag closures for use in the field use a pair of heated belts to produce a machine-direction seal. Other apparatus producing machine-direction heat seals are disclosed in the following related applications:
APPARATUS FOR SEALING A HEM IN A MOVING WEB OF FILM USING ANGULARLY ORIENTED HOT WHEELS, Herrington et al, Ser. No. 904,449 filed Sept. 8, 1986; APPARATUS FOR SEALING A HEM IN A MOVING WEB OF FILM, Herrington, Ser. No. 904,441, filed Sept. 8, 1986; APPARATUS FOR PRODUCING A MACHINE DIRECTION HEAT SEAL, Herrington, Ser. No. 904,444 filed Sept. 8, 1986; and APPARATUS FOR PRODUCING MACHINE-DIRECTION HEAT SEALS, Herrington, Ser. No. 904,445, filed Sept. 8, 1986.
The present invention is an improvement on the inventions disclosed in the above-identified related applications.